DE 44 37 122 C2 describes a safety plug which comprises a housing having a printed circuit board, surge voltage protector, a solder preform which is fused upon overshooting of a specific temperature of the surge voltage protector, a slider, a spring, a ground plate and a signalling element, a spring arm attached to the slider.
The coarse protection is realized in a known way by means of a surge voltage protector. The fail-safe mechanism connected to the surge voltage protector realizes thermal protection in the case of overloading of the surge voltage protector by short-circuiting the telecommunication wires a, b to ground. This shortcircuit mechanism is realized by a slider via which a red signalling element emerges from the plug in a plainly visible fashion at the rear of the plug when a case of surge voltage occurs.
The fused plug is of complicated design and its assembly requires substantial outlay on manipulation and time.